Analog Circuits; Attenuator - Fluke 93 Service Manual

3-14
CIRCUIT DESCRIPTIONS
3,4
ANALOG
CIRCUITS
(A2)
3.4.1
Introduction
This
paragraph
describes the
circuits or>
the
analog
A2
PCB
in detail.
Refer
to
drcuit
diagrams A2a.
A2b,
and A2c
(figures 10.5, 10.6,
and
10.7
in
chapter
10).
3.4.2
Overview analog
circuits
The
analog
A2
PCB
contains several
functional parts:
•
circuits In
the
acquisition pati
-
attenuator sections
•
EXTernal (banana)
Input/output
circuitry
•
Analog ASIC and
AOC
circuitry
•
control
circuitry
-
signal
generator
•
power
supply
and
battery
charger
Each
of
these
parts
will
be
described
separately.
First
a
short Introduction
is
given, followed
by a
detailed description.
3.4.3
ATTENUATOR
sections,
CHANNEL
A
and B
-
Introduction
See
figure
3.7.
The
attenuator sections of
both
channels
A
and B
are
identical.
In
the
following only char^nel
A
is
described.
The
corresponcSng compor>ents
for
channel
B have
the
same
numboiing, except
the
second number,
vrfiichis
'T instead
of
' 2
'.
For example:
R2202
in
channel
A
corresponds
with
R2102
fn
channel
B.
The
attenuator section consists of a
ntgh
frequency
(here
after
referred to
as
H.F.)
path
and
a low
frequency
(here
after referred to
as
LF.) path,
which are combined
again
in
the
impedance
converter
(see
figure 3.7).
To
get
a
flat
frequency
charactehstlc, both paths must
overlap
over a wide frequency
range.
Circuits
are provided
for automatic
offset
compensation.
The
output
of
the attenuator sections
of
channel
A
and
B
is
processed
further
by the
A-ASIC.